Cyclic monocarbonate bishaloformates

ABSTRACT

Cyclic monocarbonate bischloroformates are prepared by the reaction of a carbonyl halide such as phosgene with a bridged substituted resorcinol or hydroquinone such as bis(2,4-dihydroxy-3-methylphenyl)methane or bis(2,5-dihydroxy-3,4,6-trimethylphenyl)methane in the presence of aqueous alkali metal hydroxide. The cyclic monocarbonate bischloroformates may be used for the preparation of linear or cyclic polycarbonates containing cyclic carbonate structural units, which may in turn be converted to crosslinked polycarbonates.

This application is a division of copending application Ser. No.07/164,593, filed Mar. 7, 1988 now abandoned, which in turn is adivision of Ser. No. 07/29,515, filed Mar. 24, 1987 now U.S. Pat. No.4,767,840.

This invention relates to crosslinked polycarbonates and precursorstherefor. More particularly, it relates to monocarbonate bishaloformatessuitable for polycarbonate crosslinking.

Polycarbonates are well known polymers which have good propertyprofiles, particularly with respect to impact resistance, electricalproperties, optical clarity, dimensional rigidity and the like. Thesepolymers are generally linear, but can be made with branched sites toenhance their properties in specific ways. Low levels of branching aregenerally incorporated into the resin by copolymerizing into the polymerbackbone a polyfunctional reagent to yield a thermoplastic polycarbonateresin with enhanced rheological properties and melt strength which makeit particularly suitable for such types of polymer processing proceduresas the blow molding of large, hollow containers and the extrusion ofcomplex profile forms. Special manufacturing runs must be set aside toprepare these branched polycarbonate resins.

Sufficiently higher levels of branching sites in the resin will causeresin chains actually to join to each other to form partially or fullycrosslinked resin networks which will no longer be thermoplastic innature and which are expected to exhibit enhancements over correspondinglinear resins in physical properties and/or in their resistance toabusive conditions, such as exposure to organic solvents. A wide varietyof means have been employed to produce crosslinking in polycarbonateresins. They generally involve the incorporation of a suitably reactivechemical group into the resin chain at its time of manufacture, as anadditive to the resin after manufacture, or both. These reactive groupsand the reactions they undergo are generally different from thosecharacteristic of polycarbonate resins themselves and therefore tend tohave detrimental side effects on the physical and/or chemical propertiesof the polymer. The conventional test used to judge the success of thesemeans for crosslinking is to observe the formation of gels due to thecrosslinked material when a resin sample is mixed with a solvent, suchas methylene chloride, in which normal linear polycarbonate resin ishighly soluble.

By the present invention, compounds are provided which may beincorporated in conventional polycarbonate reaction mixture to providecarbonate groups as branching or crosslinking sites in the polymers.(For brevity, the term "crosslinking" as used hereinafter will denoteboth branching and crosslinking.) Said compounds are suitable forincorporation either in linear or cyclic polycarbonate reactionmixtures. There are also provided linear and cyclic polycarbonatesprepared by such reactions, as well as related crosslinkedpolycarbonates.

In one of its aspects, the present invention include cyclicmonocarbonate bishaloformates having the formula ##STR1## wherein:

X¹ is R³ CH, S, SO or SO₂ ;

R¹ is C₁₋₄ alkyl or halo;

R² is hydrogen, C₁₋₄ alkyl or halo;

R³ is hydrogen or an alkyl, cycloalkyl or aryl radical;

one of Z¹ and Z² is hydrogen, C₁₋₄ alkyl or halo and the other is##STR2## and

X² is chlorine or bromine.

The R¹ groups in the monocarbonate bishaloformates of this invention maybe C₁₋₄ alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butylor t-butyl, or halogen atoms such as chlorine and bromine. The presenceof a relatively bulky substituent of this type is critical to avoidcondensation of the haloformate groups to carbonate groups, which isfrequently accompanied by formation of gel in large amounts. Methylgroups (especially) and chlorine and bromine atoms are preferred. The R²groups may be hydrogen or alkyl or halo groups similar to R¹.

The linking X¹ radical may be methylene, substituted methylene, sulfur,sulfoxy or sulfone, wherein the R³ substituents on any substitutedmethylene radicals may be alkyl, cycloalkyl or aryl. Most often, suchsubstituents contain up to about 7 carbon atoms. Unsubstituted methyleneis frequently preferred.

Of the Z¹ and Z² values, one must be ##STR3## wherein X² is chlorine orbromine and is preferably chlorine, and the other must be hydrogen,alkyl or halo as defined for R². Thus, the monocarbonate bishaloformatesof the invention may be considered as being derived from bridgedsubstituted resorcinols and hydroquinones of the formulas ##STR4##respectively, wherein R⁴ is hydrogen, C₁₋₄ alkyl or halo as previouslydefined for R².

The cyclic monocarbonate bishaloformates of this invention may beprepared by reacting a bridged substituted resorcinol or hydroquinone offormula II or III with a stoichiometric excess of a carbonyl halide ofthe formula CO(X²)₂ (i.e., phosgene or carbonyl bromide) in the presenceof an aqueous alkali metal hydroxide solution. This reaction, which isanother aspect of the invention, is typically conducted at a temperaturein the range of about 0°-35° C.

The bridged substituted resorcinols and hydroquinones may be prepared byknown methods, such as the reaction of the correspondingdihydroxyaromatic compounds (e.g., 2-methylresorcinol ortrimethylhydroquinone) with formaldehyde or sulfur dichloride, followedwhen appropriate by oxidation of divalent sulfur to a sulfoxide orsulfone group. The preparation of sulfur- and sulfoxy-bridged compoundsis disclosed, for example, in U.S. Pat. Nos. 3,857,896 and 3,881,931,and of methylene-bridged compounds in copending, commonly ownedapplication Ser. No. 913,908, filed Oct. 1, 1986, now U.S. Pat. No.4,794,160, the disclosures of which are incorporated by referenceherein. The following example illustrates the preparation ofmethylene-bridged compounds.

EXAMPLE 1

To a solution of 248.14 parts by weight (2 moles) of 2-methylresorcinolin one liter of 2M aqueous hydrochloric acid was added 32.6 parts of 38%aqueous formaldehyde solution (0.4 mole of formaldehyde). The mixturewas stirred for two hours at about 20° C., whereupon a white solidprecipitated. It was removed by filtration, washed several times withwater and dried. The product was shown by infrared and nuclear magneticresonance spectroscopy to be the desiredbis(2,4-dihydroxy-3-methylphenyl)methane. The yield was 49.2 parts, or50% of theoretical.

In one embodiment of the method for preparing cyclic monocarbonatebishaloformates, gaseous phosgene is passed into a solution of thebridged substituted resorcinol or hydroquinone in a substantiallynon-polar organic liquid which forms a two-phase system with water. Theidentity of the liquid is not critical, provided it possesses the statedproperties. Illustrative liquids are aromatic hydrocarbons such astoluene and xylene; substituted aromatic hydrocarbons such aschlorobenzene, o-dichlorobenzene and nitrobenzene; chlorinated aliphatichydrocarbons such as chloroform and methylene chloride; and mixtures ofthe foregoing with ethers such as tetrahydrofuran. Methylene chloride isfrequently preferred.

Phosgene passage in this embodiment is generally at a temperature ofabout 10°-35° C. and preferably at about room temperature. There issimultaneously added an aqueous alkali metal hydroxide solution (e.g.,sodium hydroxide or potassium hydroxide, with sodium hydroxide beingpreferred) having a concentration in the range of about 2-10M. Theaddition rate of the alkali metal hydroxide is adjusted so as to providea pH in the range of about 3-9.

A second embodiment is to condense phosgene with the solution of thebridged substituted resorcinol or hydroquinone at a temperature belowthe condensation temperature of phosgene, typically about 0° C., andsubsequently to add sodium hydroxide while warming the mixture to effectreflux of phosgene. In either procedure, the amount of phosgene employedis about 20-100% excess over the stoichiometric amount of 3 moles permole of bridged substituted resorcinol or hydroquinone required forformation of the monocarbonate bishaloformate.

Following the reaction, excess phosgene is ordinarily removed byconventional means such as nitrogen purging. The cyclic monocarbonatebishaloformate may then be dried and isolated, also by conventionalmeans.

The preparation of the cyclic monocarbonate bishaloformates of thisinvention is illustrated by the following examples.

Example 2

A mixture of 50 ml. of methylene chloride and 2 grams (7.7 mmol.) ofbis(2,4-dihydroxy-3-methylphenyl)-methane was cooled in an ice bath to0° C. and 4.6 grams (45 mmol.) of phosgene was added. The mixture wasallowed to warm to room temperature, with stirring, over 15 minutes as125 mmol. of 5M aqueous sodium hydroxide solution was added. Phosgenereflux was maintained by use of a condenser containing solid carbondioxide and acetone.

When sodium hydroxide addition was complete, stirring was continued for10 minutes at room temperature after which excess phosgene was removedby purging with nitrogen. The organic layer was separated, washed threetimes with dilute aqueous hydrochloric acid solution, dried with phaseseparation paper and vacuum stripped to yield 2.27 grams (72%theoretical) of the desired cyclic monocarbonate bishcloroformate as atan solid. The molecular structure of the product was confirmed byproton nuclear magnetic resonance spectroscopy and field desorption massspectroscopy.

Example 3

Phosgene, 10 grams (100 mmol.), was passed at 0.5 gram per minute, withstirring, into a solution of 6.32 grams (20 mmol.) ofbis(2,5-dihydroxy-3,4,6-trimethylphenyl)methane in 100 ml. of methylenechloride. There was simultaneously added a 5M aqueous sodium hydroxidesolution at a rate of maintain the pH in the range of 4-9. Stirring wascontinued for 15 minutes after phosgene addition was complete, afterwhich excess phosgene was removed by nitrogen purging. Upon workup asdescribed in Example 2, there was obtained 5.75 grams (62% oftheoretical) of the desired cyclic monocarbonate bischloroformate. Itsstructure was confirmed by reaction with methanol in the presence oftriethylamine to yield the corresponding bis(methyl carbonate), followedby proton nuclear magnetic resonance spectroscopy.

The cyclic monocarbonate bishaloformates of this invention may behomopolymerized or incorporated in conventional reaction mixtures forthe preparation of linear or cyclic polycarbonates. The resultingproducts are polycarbonates comprising cyclic carbonate structural unitsof the formula ##STR5## optionally in combination with units of theformula ##STR6## wherein A¹ is a divalent aromatic radical and R¹, R²,R⁴ and X¹ are as previously defined. These polycarbonates are anotheraspect of the invention.

In formula IV, the carbonate oxygen atoms and R⁴ radicals are linked tothe aromatic rings in positions corresponding to those in formulas IIand III. That is, one of the two in each ring is in the meta-position tothe cyclic carbonate oxygen atom and the other is in the parapositionthereto.

As previously noted, the A¹ values are divalent aromatic radicals. Theypreferably have the formula

    --A.sup.2 --Y--A.sup.3 --,                                 (VI)

wherein each of A² and A³ is a monocyclic divalent aromatic radical andY is a bridging radical in which one or two atoms separate A² from A³.The free valence bonds in formula II are usually in the meta or parapositions of A¹ and A² in relation to Y.

In formula VI, the A² and A³ values may be unsubstituted phenylene orsubstituted derivatives thereof, illustrative substituents (one or more)being alkyl, alkenyl, halo (especially chloro and/or bromo), nitro,alkoxy and the like. Unsubstituted phenylene radicals are preferred.Both A² and A³ are preferably p-phenylene, although both may be o- orm-phenylene or one o- or m-phenylene and the other p-phenylene.

The bridging radical, Y, is one in which one or two atoms, preferablyone, separate A² from A³. It is most often a hydrocarbon radical andparticularly a saturated radical such as methylene, cyclohexylmethylene,2-[2.2.1]-bicycloheptylmethylene, ethylene, isopropylidene,neopentylidene, cyclohexylidene, cyclopentadecylidene, cyclododecylideneor adamantylidene, especially a gemalkylene (alkylidene) radical. Alsoincluded, however, are unsaturated radicals and radicals which containatoms other than carbon and hydrogen; for example,2,2-dichloroethylidene, carbonyl, phthalidylidene, oxy, thio, sulfoxyand sulfone.

The A¹ values may be considered as being derived from dihydroxyaromaticcompounds of the formula HO--A¹ --OH, preferably bisphenols of theformula HO--A² --Y--A³ --OH. The following dihydroxy compounds areillustrative:

Resorcinol

4-Bromoresorcinol

Hydroquinone

4,4'-Dihydroxybiphenyl

1,6-Dihydroxynaphthalene

2,6-Dihydroxynaphthalene

Bis(4-hydroxyphenyl)methane

Bis(4-hydroxyphenyl)diphenylmethane

Bis(4-hydroxyphenyl)-1-naphthylmethane

1,1-Bis(4-hydroxyphenyl)ethane

1,2-Bis(4-hydroxyphenyl)ethane

1,1-Bis(4-hydroxyphenyl)-1-phenylethane

2,2-Bis(4-hydroxyphenyl)propane ("bisphenol A")

2-(4-Hydroxyphenyl)-2-(3-hydroxyphenyl) propane

2,2-Bis(4-hydroxyphenyl)butane

1,1-Bis(4-hydroxyphenyl)isobutane

1,1-Bis(4-hydroxyphenyl)cyclohexane

1,1-Bis(4-hydroxyphenyl)cyclododecane

Trans-2,3-bis(4-hydroxyphenyl)-2-butene

2,2-Bis(4-hydroxyphenyl)adamantane

α,α'-Bis(4-hydroxyphenyl)toluene

Bis(4-hydroxyphenyl)acetonitrile

2,2-Bis(3-methyl-4-hydroxyphenyl)propane

2,2-Bis(3-ethyl-4-hydroxyphenyl)propane

2,2-Bis(3-n-propyl-4-hydroxyphenyl)propane

2,2-Bis(3-isopropyl-4-hydroxyphenyl)propane

2,2-Bis(3-sec-butyl-4-hydroxyphenyl)propane

2,2-Bis(3-t-butyl-4-hydroxyphenyl)propane

2,2-Bis(3-cyclohexyl-4-hydroxyphenyl)propane

2,2-Bis(3-allyl-4-hydroxyphenyl)propane

2,2-Bis(3-methoxy-4-hydroxyphenyl)propane

2,2-Bis(3,5-dimethyl-4-hydroxyphenyl)propane

2,2-Bis(2,3,5,6-tetramethyl-4-hydroxyphenyl)propane

2,2-Bis(3,5-dichloro-4-hydroxyphenyl)propane

2,2-Bis(3,5-dibromo-4-hydroxyphenyl)propane

2,2-Bis(2,6-dibromo-3,5-dimethyl-4-hydroxyphenyl)propane

α,α-Bis(4-hydroxyphenyl)toluene

α,α,α',α'-Tetramethyl-α,α'-bis(4-hydroxyphenyl)-p-xylene

2,2-Bis(4-hydroxyphenyl)hexafluoropropane

1,1-Dichloro-2,2-bis(4-hydroxyphenyl)ethylene

1,1-Dibromo-2,2-bis(4-hydroxyphenyl)ethylene

1,1-Dichloro-2,2-bis(5-phenoxy-4-hydroxyphenyl)ethylene

4,4'-Dihydroxybenzophenone

3,3-Bis(4-hydroxyphenyl)-2-butanone

1,6-Bis(4-hydroxyphenyl)-1,6-hexanedione

Ethylene glycol bis(4-hydroxyphenyl)ether

Bis(4-hydroxyphenyl)ether

Bis(4-hydroxyphenyl)sulfide

Bis(4-hydroxyphenyl)sulfoxide

Bis(4-hydroxyphenyl)sulfone

Bis(3,5-dimethyl-4-hydroxyphenyl)sulfone

9,9-Bis(4-hydroxyphenyl)fluorene

2,7-Dihydroxypyrene

6,6'-Dihydroxy-3,3,3',3'-tetramethylspiro(bis)indane ("spirobiindanebisphenol")

3,3-Bis(4-hydroxyphenyl)phthalide

2,6-Dihydroxydibenzo-p-dioxin

2,6-Dihydroxythianthrene

2,7-Dihydroxyphenoxathiin

2,7-Dihydroxy-9,10-dimethylphenazine

3,6-Dihydroxydibenzofuran

3,6-Dihydroxydibenzothiophene

2,7-Dihydroxycarbazole.

Bisphenol A is often preferred for reasons of availability andparticular suitability for the purposes of the invention.

The polycarbonates of this invention include linear polycarbonates. Theymay be prepared by employing the cyclic monocarbonate bishaloformates ofthe invention in conventional polycarbonate-forming reactions.

For example, the cyclic monocarbonate bishaloformate may be addedconcurrently with phosgene to a heterogeneous mixture including abisphenol solution, whereupon both the phosgene and the cyclicmonocarbonate bishaloformate will react with the bisphenol to form alinear polycarbonate. Preferably, however, the cyclic monocarbonatebishaloformate is combined with a bishaloformate of one of thepreviously defined dihydroxyaromatic compounds for conversion topolycarbonates by the action of an interfacial polycarbonate formationcatalyst and an acid acceptor, according to general methods known in theart. Reference is made, for example, to U.S. Pat. Nos. 3,189,640 and4,025,489, as well as copending, commonly owned application Ser. No.917,751, filed Oct. 10, 1986, now U.S. Pat. No. 4,737,573, thedisclosures of which are incorporated by reference herein.

Another species of polycarbonates of this invention consists of cyclicpolycarbonate oligomers. These may be single oligomeric compounds suchas those disclosed in the following U.S. Pat. Nos.:

3,155,683

3,274,214

3,386,954

3,422, 119.

Cyclic polycarbonate oligomer mixtures may also be prepared. Mixtures ofthis type are disclosed in U.S. Pat. No. 4,644,053, the disclosure ofwhich is incorporated by reference herein.

The cyclic oligomer ,mixtures consist essentially of oligomers havingdegrees of polymerization from 2 to about 30 and preferably to about 20,with a major proportion being up to about 12 and a still largerproportion up to about 15. Since they are mixtures of oligomers havingvarying degrees of polymerization, these compositions have relativelylow melting points as compared to single compounds. The cyclic oligomermixtures are generally liquid at temperatures above 300° C. and mostoften at temperatures above 225° C.

It has been discovered that the cyclic oligomer mixtures contain verylow proportions of linear oligomers. In general, no more than about 10%by weight, and most often no more than about 5% (if any), of such linearoligomers are present. The mixtures also usually contain at most lowpercentages (frequently less than 30% and preferably no higher thanabout 20%) of polymers (linear or cyclic) having a degree ofpolymerization greater than about 30. Such polymers are frequentlyidentified hereinafter as "high polymer". These properties, coupled withthe relatively low melting points and viscosities of the cyclic oligomermixtures, contribute to their utility as resin precursors, especiallyfor high molecular weight resins.

The cyclic oligomer mixtures of this invention may be prepared by amethod which comprises contacting (A) a composition comprising at leastone cyclic monocarbonate bishaloformate of formula I with

(B) at least one oleophilic aliphatic or heterocyclic tertiary amine and

(C) an aqueous alkali or alkaline earth metal hydroxide or carbonatesolution;

said contact being effected under conditions whereby reagent A ismaintained in low concentration in (D) a substantially non-polar organicliquid which forms a two-phase system with water.

Reagent A comprises (1) at least one cyclic monocarbonatebischloroformate of the invention (reagent A-1). It may also contain (2)at least one bishaloformate of the formula

    A.sup.1 (OCOX.sup.2).sub.2,                                (VII)

wherein A¹ and X² are as defined hereinabove (reagent A-2), and,optionally, (3) at least one diol having the formula

    R.sup.5 (OH).sub.2,                                        (VIII)

wherein R⁵ is a divalent aliphatic or alicyclic radical, or an alkalimetal salt thereof (reagent A-3), as well as other compounds, includingbishaloformate oligomers. The proportion of cyclic monocarbonatebishaloformate in admixture with such other compounds will depend on theamount of crosslinking desired in the final linear polycarbonate and isgenerally at least about 1 and preferably about 2-10 mole percent.

While the X² values in formulas I and VII may be chlorine or bromine,the bischloroformates, in which X² is chlorine, are most readilyavailable and their use is therefore preferred. (Frequent reference tobischloroformates will be made hereinafter, but it should be understoodthat other bishaloformates may be substituted therefor as appropriate.)Suitable bis(active hydrogen) compounds of formula VIII (reagent A-3)include dihydroxyaromatic compounds having divalent radicals which areidentical to or different from the corresponding divalent radicals inthe compound of formula VII, as well as other diols. When such diols (ortheir alkali metal salts) are present, they generally comprise up toabout 50%, most often up to about 20% and preferably up to about 10%, ofthe total of reagents A-2 and A-3.

Most preferably, reagent A consists essentially of reagents A-1 and A-2or of a mixture of reagent A-1 and reagents A-2 and A-3 in which A¹ andR⁵ are identical, as noted hereinafter. Any cyclic oligomers containingdivalent aliphatic radicals or their vinylogs are prepared by using amixture of compounds identifiable as reagent A-2.

Reagent A-2 may be a bischloroformate in substantially pure, isolatedform. It is frequently preferred, however, to use a crudebischloroformate product. Suitable crude products may be prepared by anyknown methods for bischloroformate preparation. Typically, at least onebisphenol is reacted with phosgene in the presence of a substantiallyinert organic liquid, as disclosed in the following U.S. Pat. Nos.:

3,255,230

3,312,661

3,966,785

3,974,126.

The disclosures of these patents are incorporated by reference herein.

In addition to the bisphenol bischloroformate, such crudebishcloroformate products may contain oligomer bischloroformates. Mostoften, a major proportion of the crude product comprises monomer, dimerand trimer bischloroformate. Higher oligomer bischloroformates, andmonochloroformates corresponding to any of the aforementionedbischloroformates, may also be present, preferably only in relativelysmall amounts.

More preferably, the preparation of the crude bischloroformate producttakes place in the presence of aqueous alkali. The pH of the reactinmixture may be up to about 12. It is generally found, however, that theproportion of high polymer in the cyclic oligomer mixture is minimizedby employing a crude bischloroformate product comprising a major amountof bisphenol bischloroformate and only minor amounts of any oligomerbischloroformates. Such products may be obtained by the method disclosedin U.S. Pat. No. 4,638,077, the disclosure of which is also incorporatedby reference herein. In that method, phosgene is passed into a mixtureof a substantially inert organic liquid and a bisphenol, said mixturebeing maintained at a temperature within the range of about 10°-40° C.,the phosgene flow rate being at least 0.15 equivalent per equivalent ofbisphenol per minute when the temperature is above 30° C. An aqueousalkali metal or alkaline eaerth metal base solution is simutaneouslyintroduced as necessary to maintain the pH in the range of about0.5-8.0. By this method, it is possible to prepare bischloroformate inhigh yield while using a relatively small proportion of phosgene,typically up to about 1.1 equivalent per equivalent of bisphenol.

When one of these methods is employed, it is obvious that the crudebishcloroformate product will ordinarily be obtained as a solution in asubstantially non-polar organic liquid such as those disclosedhereinafter. Depending on the method of preparation, it may be desirableto wash said solution with a dilute aqueous acidic solution to removetraces of base used in preparation.

The tertiary amines useful as reagent B("tertiary" in this contextdenoting the absence of N-H bonds) generally comprise those which areoleophilic (i.e., which are soluble in and highly active in organicmedia, especially those used in the oligomer preparation method), andmore particularly those which are useful for the formation ofpolycarbonates. Reference is made, for example, to the tertiary aminesdisclosed in U.S. Pat. Nos. 4,217,438 and 4,368,315, the disclosures ofwhich are also incorporated by reference herein. They include aliphaticamines such as triethylamine, tri-n-propylamine, diethyl-n-propylamineand tri-n-butylamine and highly nucleophilic heterocyclic amines such as4-dimethylaminopyridine (which, for the purposes of this invention,contains only one active amine group). The preferred amines are thosewhich dissolve preferentially in the organic phase of the reactionsystem; that is, for which the organic-aqueous partition coefficient isgreater than 1. This is true because intimate contact between the amineand reagent A is essential for the formation of the cyclic oligomermixture. For the most part, such amines contain at least about 6 andpreferably about 6-14 carbon atoms.

The amines most useful as reagent B are trialkylamines containing nobranching on the carbon atoms in the 1- and 2-positions. Especiallypreferred are tri-n-alkylamines in which the alkyl groups contain up toabout 4 carbon atoms. Triethylamine is most preferred by reason of itsparticular availability, low cost, and effectiveness in the preparationof products containing low percentages of linear oligomers and highpolymers.

Reagent C is an aqueous alkali or alkaline earth metal hydroxide orcarbonate solution, such as lithium, sodium, potassium or calciumhydroxide or sodium or potassium carbonate. It is most often lithium,sodium or potassium hydroxide, with sodium hydroxide being preferredbecause of its availability and relatively low cost. The concentrationof the solution is not critical and may be about 0.1-16M, preferablyabout 0.1-10M.

The fourth essential component (component D) in the cyclic oligomerpreparation method is a substantially non-polar organic liquid whichforms a two-phase system with water. Suitable liquids are definedhereinabove with reference to the preparation of cyclic monocarbonatebishaloformates.

To prepare the cyclic oligomer mixture according to the above-describedmethod, the reagents and components are maintained in contact underconditions whereby reagent A is present in low concentration. Actualhigh dilution conditions, requiring a large proportion of component D,may be employed but are usually not preferred for cost and conveniencereasons. Instead, simulated high dilution conditions known to thoseskilled in the art may be employed. For example, in one embodiment ofthe method reagent A (and optionally other reagents) are added graduallyto a reaction vessel containing solvent.

Although addition of reagent A neat (i.e., without solvents) is withinthe scope of this embodiment, it is frequently inconvenient because manybischloroformates are solids. Therefore, it is preferably added as asolution in a portion of component D, especially when it consistsessentially of reagents A-1 and A-2. The proportion of component D usedfor this purpose is not critical; about 25-75% by weight, and especiallyabout 40-60%, is preferred.

The reaction temperature is generally in the range of about 0°-50° C. Itis most often about 0°-40° C. and preferably 20°-40° C.

For maximization of the yield and purity of cyclic oligomers as opposedto high polymer and insoluble and/or intractable by-products, it ispreferred to use not more than about 1.5 mole of reagent A, calculatedas bischloroformate (and bisphenol or salt thereof if present), perliter of component D in the reaction system, including any liquid usedto dissolve reagent A. Preferably, about 0.003-1.0 mole of reagent A isused when it consists entirely of reagents A-1 and (optionally) A-2 andno more than about 0.5 mole is used when it includes reagent A-3. Itshould be noted that this is not a molar concentration in component Dwhen reagent A is added gradually, since said reagent is consumed as itis added to the reaction system.

The molar proportions of the reagents constitute another importantfeature for yield and purity maximization. The preferred molar ratio ofreagent B to the total of reagent A-1 and any reagent A-2 (calculated asbischloroformate) is about 0.1-1.0:1 and most often about 0.15-0.6:1,and that of reagent C to the total of reagent A-1 and any reagent A-2 isabout 2-5:1 and most often about 4-5:1. When a combination includingreagent A-3 is used, the preferred molar ratio for reagent B is about0.1-0.5:1. The preferred ratio for reagent C is the same as above,including any alkali metal hydroxide used to form an alkali metal saltused as reagent A-3.

The use of reagent A-3 comprising a bisphenol alkali metal salt is ofparticular value when it is desired to minimize the amount of phosgenerequired for overall production of cyclic polycarbonates. When reagentA-1 and (optionally) reagent A-2 are used alone, half the phosgene usedfor bischloroformate formation is lost by hydrolysis upon conversion ofthe bischloroformate to cyclics. On the other hand, each chloroformatemoiety can theoretically react with a bisphenol salt moiety to form acarbonate group if the latter is present in sufficient amount. It isalso frequently found that the proportion of cyclic dimer in the productis maximized by use of reagent A-3.

In practice, it is generally found that incorporation of reagent A-3into cyclics under these conditions is incomplete. Thus, removal of anyunreacted bisphenol as its alkali metal salt may be necessary.

Following their preparation, the cyclic oligomers may be separated fromat least a portion of the high polymer and insoluble material present.When other reagents are added to reagent C and the preferred conditionsand material proportions are otherwise employed, the cyclic oligomermixture (obtained as a solution in the organic liquid) typicallycontains less than 30% by weight and frequently less than about 20% ofhigh polymer and insoluble material. When all of the preferredconditions described hereinafter are employed, the product may contain10% or even less of such material. Depending on the intended use of thecyclic oligomer mixture, the separation step may then be unnecessary.

Therefore, a highly preferred method for preparing the cyclic oligomermixture comprises the single step of conducting the reaction using asreagent B at least one aliphatic or heterocyclic tertiary amine which,under the reaction conditions, dissolves preferentially in the organicphase of the reaction system, and gradually adding reagent A and atleast a portion of reagents B and C simultaneously to a substantiallynon-polar organic liquid (component D) or to a mixture of said liquidwith water, said liquid or mixture being maintained at a temperature inthe range of about 0°-50° C.; the amount of reagent A used being up toabout 0.7 mole for each liter of component D present in the reactionsystem, and the total molar proportions of reagents A, B and C beingapproximately as follows:

B:A-0.06-2.0:1

C:A-4-5:1;

and recovering the cyclic oligomers thus formed.

A factor of some importance in this embodiment is the concentration ofavailable reagent B, which should be maintained at a level as constantas possible during the entire addition period for reagents A-1 and A-2(if any). If all of reagent B is present in the reaction vessel intowhich reagents A-1 and (optionally) A-2 are introduced, itsconcentration steadily decreases, principally by dilution. On the otherhand, if reagent B is introduced continuously or in equal incrementsduring introduction of reagents A-1 and (optionally) A-2, its availableconcentration is initially low and increases more or less steadilyduring the addition period. These fluctuations can result in a high andconstantly varying proportion of high polymer in the product.

When reagent A-3 is employed in this embodiment, cyclics yield isusually optimized if said reagent is absent from the portion of reagentA added near the end of the reaction. In other words, it is oftenpreferred that any batch be terminated by a period of addition ofreagent A consisting essentially of reagents A-1 and (optionally) A-2.

It has been found advantageous to introduce reagent B in one initiallarge portion, usually about 40-95% and preferably about 40-75% byweight of the total amount, followed by incremental or continuousaddition of the balance thereof. By this procedure, the concentration ofavailable reagent B is maintained at a fairly constant level in theorganic phase during the entire addition period, and it is possible tominimize the proportion of high polymer in the product. Typically, highpolymer content is 20% or less when this mode of addition is used.

Under these conditions, it is usually advantageous for the reactionvessel to initially contain about 5-40% and preferably about 5-30% oftotal reagent C. The balance thereof is also introduced continuously orincrementally. As in the embodiment previously described, anotherportion of component D may serve as a solvent for reagent A.

Among the other principal advantages of this preferred embodiment arethe non-criticality of the degree of dilution of the reagents and theability to complete the addition and reaction in a relatively shorttime, regardless of reaction scale. It ordinarily takes only about 25-30minutes to complete cyclic oligomer preparation by this method, and thecyclic oligomer yield may be 85-90% or more. By contrast, use of a lesspreferred embodiment may, depending on reaction scale, require anaddition period as long as 8-10 hours and the crude product may containsubstantial proportions of linear by-products with molecular weights ofabout 4,000-10,000, which, if not removed, may interfere with subsequentpolymerization of the cyclic oligomers by acting as chain transferagents.

In this preferred embodiment, the pH of the aqueous phase of thereaction mixture is typically in the range of about 9-14 and preferablyabout 12. When reagent A (and optionally reagent B) is added to all ofthe reagent C, on the other hand, the initial pH remains on the order of14 during essentially the entire reaction period.

When separation of impurities is desired, it may be effected byconventional operations such as combining the crude product, as a solidor in solution, with a non-solvent for said impurities. Illustrativenon-solvents include ketones such as acetone and methyl isobutyl ketoneand esters such as methyl acetate and ethyl acetate. Acetone is aparticularly preferred non-solvent.

Recovery of the cyclic oligomers normally means merely separating thesame from diluent (by known methods such as vacuum evaporation) and,optionally, from high polymer and other impurities. As previouslysuggested, the degree of sophistication of recovery will depend on suchvariables as the intended end use of the product.

The preparation of cyclic polycarbonate oligomer mixtures according tothis invention is illustrated by the following example.

Example 4

A mixture of 150 ml. of methylene chloride, 62.5 mg. of triethylamineand 2.5 ml. of 5M aqueous sodium hydroxide solution was prepared andthere were simultaneously added thereto with stirring, over 35 minutes,a solution of 1 gram (2.45 mmol.) of the cyclic monocarbonatebischloroformate of Example 2 and 17.22 grams (48.78 mmol.) of bisphenolA bischloroformate in 50 ml. of methylene chloride, 47.5 ml. of 5Maqueous sodium hydroxide solution and 1.19 grams (total 12.3 mmol.) oftriethylamine. The aqueous and organic phases were separated and theaqueous layer was washed with methylene chloride. The combined organicphases were washed once with dilute aqueous sodium hydroxide, twice withaqueous hydrochloric acid, once again with sodium hydroxide and twicewith water, and dried over magnesium sulfate. Upon filtration, vacuumstripping and drying in an oven, there was obtained a white solid whichwas shown by high pressure liquid chromatography to comprise the desiredcyclic oligomer mixture. The yield was about 85%.

The cyclic oligomer compositions of this invention, incorporating unitsof formula V, may be converted to crosslinked polycarbonates.Accordingly, the present invention includes a method for the preparationof a crosslinked resinous composition which comprises contacting atleast one of the previously defined cyclic oligomer compositions with apolycarbonate formation catalyst at a temperature up to about 350° C.,as well as crosslinked compositions prepared by said method. The methodis similar to that described in the aforementioned U.S. Pat. No.4,644,053 and in copending, commonly owned application Ser. No. 888,673,filed July 24, 1986, now U.S. Pat. No. 4,740,583, the disclosure ofwhich is incorporated by reference herein. The oligomer compositions mayfrequently be employed without separation of high polymer therefrom, butif desired, high polymer may be removed as previously described.

The polycarbonate formation catalysts which can be used in the resinformation method of this invention include various bases and Lewisacids. It is known that basic catalysts may be used to preparepolycarbonates by the interfacial method, as well as bytransesterification and from cyclic oligomers. Reference is made to theaforementioned U.S. Pat. Nos. 3,155,683, 3,274,214, 4,217,438 and4,368,315. Such catalysts may also be used to polymerize the cyclicoligomer compositions. Examples thereof are lithium phenoxide, lithium2,2,2-trifluoroethoxide, n-butyllithium and tetramethylammoniumhydroxide. Also useful are various weakly basic salts such as sodiumbenzoate and lithium stearate.

A particularly useful calss of Lewis bases is disclosed in U.S. Pat. No.4,605,731. It comprises numerous tetraarylborate salts, includinglithium tetraphenylborate, sodium tetraphenylboarte, sodiumbis(2,2'-biphenylene)borate, potassium tetraphenylborate,tetramethylammonium tetraphenylborate, tetra-n-butylammoniumtetraphenylborate, tetramethylphosphonium tetraphenylborate,tetra-n-butylphosphonium tetraphenylborate and tetraphenylphosphoniumtetraphenylborate. The preferred catalysts within this class are thetetra-n-alkylammonium and tetra-n-alkylphosphonium tetraphenylborates.Tetramethylammonium tetraphenylborate is particularly preferred becauseof its high activity, relatively low cost and ease of preparation fromtetramethylammonium hydroxide and an alakli metal tetraphenylborate.

Another class of particularly useful basic catalysts is disclosed incopending, commonly owned application Ser. No. 941,901, filed Dec. 15,1986, now U.S. Pat. No. 4,701,519, the disclosure of which is alsoincorporated by reference herein. It comprises polymers of containingalkali metal phenoxide and especially lithium phenoxide moieties. Theyare usually present at end groups, especially on linear polycarbonateshaving a number average molecular weight in the range of about8,000-20,000 as determined by gel permeation chromatography relative topolystyrene. Such catalysts may be produced by reacting a suitablepolymer with an alkali metal base, typically at a temperature in therange of about 200°-300° C.

The Lewis acids useful as polycarbonate formation catalysts are selectedfrom non-halide compounds and include dioctyltin oxide,triethanolaminetitanium isopropoxide, tetra(2-ethylhexyl) titanate andpolyvalent metal (especially titanium and aluminum) chelates such asbisisopropoxytitanium bisacetylacetonate (commercially available underthe trade name "Tyzor AA") and the bisisopropoxyaluminum salt of ethylacetoacetate.

The conversion of cyclic oligomers to crosslinked polymers isillustrated by the following example.

Example 5

A solution in methylene chloride of the product of Example 4 andtetraethylammonium tetraphenylborate in the amount of 0.1 mole percent,based on carbonate units in said product, was rotoevaporated to producean intimate cyclicscatalyst mixture. The mixture was heated at 250° C.for 2 hours. There was obtained a crosslinked polycarbonate which was99.1% insoluble in methylene chloride and which had a glass transitiontemperature of 175° C.

Linear polycarbonates of the present invention, incorporating structuralunits of formula V, may be crosslinked by reaction with a polycarbonateformation catalyst under conditions similar to those describedhereinabove with reference to cyclic oligomers.

What is claimed is:
 1. A cyclic monocarbonate bishalofomate having theformula ##STR7## wherein: X¹ is R³ CH, S, SO or SO₂ ;R¹ is C₁₋₄ alkyl orhalo; R² is hydrogen, C₁₋₄ alkyl or halo; R³ is hydrogen or an alkyl,cycloalkyl or aryl radical; one of Z¹ and Z² is hydrogen, C₁₋₄ alkyl orhalo and the other is ##STR8## and X² is chlorine or bromine.
 2. Abishaloformate according to claim 1 wherein X² is chlorine and R¹ ismethyl.
 3. A bishaloformate according to claim 2 wherein X¹ is CH₂.
 4. Abishaloformate according to claim 3 wherein Z¹ is ##STR9## and R² and Z²are each hydrogen.
 5. A bishaloformate according to claim 3 wherein Z²is ##STR10## and R² and Z¹ are each methyl.